The present invention relates to a viscous fluid clutch and more particularly to a viscous clutch adapted to be controlled by a remote temperature sensing element wherein an electromagnetic coil is disposed within a cavity in the shaft of the fluid clutch and an armature member is disposed within the coil and moves in response to energization of the coil. Movement of the armature member controls the fluid flow in the viscous coupling between the reservoir and the operating chamber. The armature and coil are arranged to optimize the flux path which effects movement of the armature to enable the clutch to utilize a small low power coil to effect movement of the armature.
Known remote sensing viscous fluid clutches have not optimized the flux circuit between an electromagnetic coil and an armature moved in response to the electromagnetic coil. The known prior art, such as disclosed in the Detty, U.S. Pat. No. 4,056,178, utilize a coil to control the fill and scavenge rates of a viscous clutch wherein the coil is disposed around the circumference of the shaft of the water pump. The coil surrounds the shaft and an armature member is disposed coaxially to the shaft in an axial opening in the shaft and moves in response to energization of the coil. The armature member is not located within the coil and the flux path established by the coil is required to pass through much of the magnetic material of the water pump and through a substantial portion of the shaft as well as a large air gap in order to create a magnetic field to effect movement of the armature. Such a flux path requires large amounts of energy to effect movement of the armature due to the losses occurred when the flux path passes through portions of the water pump, shaft and air gap. Such a configuration requires a larger coil which consumes more power than that described in the present application.